This invention relates to thickness measurement instruments, and in particular to ultrasound thickness measurement instruments.
In many applications it is helpful to know with accuracy the thickness of a part. A thickness measurement may be used to detect part wear and may indicate that a part should be replaced before the part mechanically fails. For example, thickness measurements are helpful in determining whether to replace pipes carrying fluids, e.g., liquids or gasses, before the pipe bursts or otherwise fails due to excessive wear. On the other hand, it is desirable to avoid replacing pipes that still have a considerable safe useful life. For this reason, the need for accuracy in the determination of the thickness of the part is paramount.
Ultrasound instruments have been used to measure the thickness of pipes and other parts. The time-of-flight (TOF) of an ultrasonic echo traveling through a part is used to determine the thickness of the part. The ultrasound velocity in the part is a known constant. Thus, the TOF provides an accurate indication of part thickness. Pulse-echo techniques are usually used for these ultrasound measurements. Instruments having dual transducers in a pitch-catch configuration may be utilized for ultrasonic thickness measurements.
Pipes and other parts often are coated with paint and other coatings that affect the propagation rate of ultrasound signals. The coating may corrode or become thin due to wear. Measurement of the thickness is needed to determine whether the coating needs to be repaired or reapplied, and whether the coated pipe should be replaced.
Ultrasound measurement of the thickness of coatings is problematic. Pulse echo ultrasound techniques rely on the time of flight (TOF) of echoes reflecting off internal features of the part. With a corroded coating, the echoes at the interface between the coating and underlying pipe often become distorted due to the corrosion. In some instances, the ultrasound instrument cannot detect an echo from the coating-pipe interface and cannot reliably measure the thickness of the coating. Accordingly, there is a long felt need for a system and method to measure the thickness of coatings on parts using ultrasound measurement techniques.